[meteorite-list] Largest Crater in the Sahara Desert and LDG

From: MexicoDoug_at_aol.com <MexicoDoug_at_meteoritecentral.com>
Date: Sat Mar 4 17:05:18 2006
Message-ID: <2b4.5abe121.313b690f_at_aol.com>

Sterling W. writes:

<< Crustal rocks have 5 or 10 times
 more fluorine than boron. Tektites should have a ratio of 1.0,
 indicating that they were heated to temperatures high enough
 to drive off most of the fluorine and leave the two halogens
 at identical levels (however low the absolute amount), and indeed
 tektites have values that "float" around 1.0 (like 0.8 to 1.2).
 The tested LDG F/B ratio is 1.0. >>

Norm, Sterling, Mark, Tracy, list,

I'm still on the fence about Libyan Desert Glass and how it fits into the
puzzle and I wanted to thank Norm for the motivation to reconsider some of it
based on the additional support that that LDG may have actually been tossed a
significant (lateral?) distance to its resting point. Norm, my thoughts on the
difference in the mechanism of formation here are basically along the lines
pursued by Wasson, that Muong Nongs (and probably LDG's) result from a different
conceptual and physical event: that while they may be clearly or partially
impacted and have received a portion of their formation from that, that
importantaly also: a major source of the energy that led to their formation was being
broiled by an overhead explosion perhaps of a manyfold-Tunguska type, or by the
same clould of incredible enery flux that formed some of the "true-to-form"
tektites. This is why I am on the fence - because I feel more comfortable with
that scenario to fall back upon.

Just want to hold on to a concept, of what tektite means to me as Norm
originally asked. While Norm argued to liberalize the definition to include LDG's,
I'm playing the conservative interpretation here like Sterling is also joining
to do. I don't disagree, just ask for one positive indication in my
preferred set of rules. Norm might just be right if we play by his rules and accept
that LDG's were chucked a good distance and thus call them tektites based on
that criterion. At minimumn LDGs are more important now as we glean more
information from them and maybe an additional piece of the endless puzzle.

I am really not quite sure why Sterling mentions the F and B assays would
tend to "identical" levels in tektites, and I while it may be my turn to split
hairs, I think this is an interesting research point, but presented inside out.
 Yes, Fluorine is generally more volatile and probably preferentially driven
off, though we should verify this is true for the source matrix solubility
before being 100% convinced. The major problem I have here is that there is
nothing magic about having them with the same concentration level as you imply, I
think this is just a coincidence on what has been looked at so far, possibly
related to the temperatures and residence times (determined by physical
constraints) in the liquid state of formation too, yes, of course, but that is as far
as I would go. That is why I think it is too great a leap of faith to
discuss why they would be "perfect tektites" based on these measurements.

Putting this [F]:[B] further under the microscope, it is also of academic
interest to compare this to the source rock - but I would never flip that around
to discuss why [F] and [B] should be identical or at a particular ratio
without knowing the initial values in the source rock, since I cannot fathom any
mechanism that would insist that tektites should have these levels "identical",
and the range you quote and attribute some special meaning to, anyway for
tektites "floating" goes below 1.0 anyway, and as a matter of fact the tektites
could easily have much lower values for this ratio than you quote, has Dr.
Koerbel and colleagues ever fired up their special Boron sensitive electrode to
check these numbers for moldavites lately?

Basically, Sterling is making a big assumption by saying that the source
rocks of the sandstone are in the range of 5 - 10 for a [F]:[B] ratio, and I think
frankly that is a poke in the dark or leap of faith at minimum. I would much
rather see someone actually go measure the [F] and [B] numbers for relatively
unaltered sandstone near the excitingly discussed crater just to check that
the ratios didn't happen to start out at values much closer to equal ... there
is significant variation on the earth.

The bottom line in my view is that the interpretation of the Fluorine and
Boron concentration numbers and ratios is meaningful for an apples to apples
comparison when the situation of the crater is not known if and only if we had
tektites (or some other glass type) formed from the LDG event then we could
measure (at least Dr. Koerbel and his colleagues could) and compare the tendencies
with the series (e.g.,LDG, hypothetical button, hypothetical splashform,etc.)
which I consider the more appropriate interpretation of this. Not take it out
of context and generalize for the whole planet and say "they should be
perfect tektites." So there are not enough numbers put on this pig, in my opinion,
and wish my disagreement on that split hair point duly noted!

Eventually I feel comfortable that we have a good chance explaining all the
curious forms of glass by considering what is jetted upwards to form
"tektites", what is heated below from explosions above, what receives the good old
"one-two" punch on the ground in the form of energy transmitted by waves propagated
as the impactor coalesces and subsequently scalded, and what gets scalded
alone by the jet of plasma like material sent upward. Given that an impact isn't
an instantaneous event, there are many possibilities to work through here,
and each one imho probably leaves its unique signature in the glasses.

Saludos, Doug
Received on Sat 04 Mar 2006 05:05:03 PM PST